DESCRIPTION

sudo allows a permitted user to execute a command as the superuser or
another user, as specified by the security policy. The real and
effective uid and gid are set to match those of the target user, as
specified in the password database, and the group vector is initialized
based on the group database (unless the -P option was specified).
sudo supports a plugin architecture for security policies and
input/output logging. Third parties can develop and distribute their
own policy and I/O logging modules to work seemlessly with the sudo
front end. The default security policy is sudoers, which is configured
via the file /etc/sudoers, or via LDAP. See the PLUGINS section for
more information.
The security policy determines what privileges, if any, a user has to
run sudo. The policy may require that users authenticate themselves
with a password or another authentication mechanism. If authentication
is required, sudo will exit if the user's password is not entered
within a configurable time limit. This limit is policy-specific; the
default password prompt timeout for the sudoers security policy is
unlimited.
Security policies may support credential caching to allow the user to
run sudo again for a period of time without requiring authentication.
The sudoers policy caches credentials for 15 minutes, unless overridden
in sudoers(5). By running sudo with the -v option, a user can update
the cached credentials without running a command.
When invoked as sudoedit, the -e option (described below), is implied.
Security policies may log successful and failed attempts to use sudo.
If an I/O plugin is configured, the running command's input and output
may be logged as well.

OPTIONS

sudo accepts the following command line options:
-A Normally, if sudo requires a password, it will read it from
the user's terminal. If the -A (askpass) option is
specified, a (possibly graphical) helper program is
executed to read the user's password and output the
password to the standard output. If the SUDO_ASKPASS
environment variable is set, it specifies the path to the
helper program. Otherwise, if /etc/sudo.conf contains a
line specifying the askpass program, that value will be
used. For example:
# Path to askpass helper program
Path askpass /usr/X11R6/bin/ssh-askpass
If no askpass program is available, sudo will exit with an
error.
-b The -b (background) option tells sudo to run the given
command in the background. Note that if you use the -b
option you cannot use shell job control to manipulate the
process. Most interactive commands will fail to work
properly in background mode.
-C fd Normally, sudo will close all open file descriptors other
than standard input, standard output and standard error.
The -C (closefrom) option allows the user to specify a
starting point above the standard error (file descriptor
three). Values less than three are not permitted. The
security policy may restrict the user's ability to use the
-C option. The sudoers policy only permits use of the -C
option when the administrator has enabled the
closefrom_override option.
-D level Enable debugging of sudo plugins and sudo itself. The
level may be a value from 1 through 9.
-E The -E (preserveenvironment) option indicates to the
security policy that the user wishes to preserve their
existing environment variables. The security policy may
return an error if the -E option is specified and the user
does not have permission to preserve the environment.
-e The -e (edit) option indicates that, instead of running a
command, the user wishes to edit one or more files. In
lieu of a command, the string "sudoedit" is used when
consulting the security policy. If the user is authorized
by the policy, the following steps are taken:
1. Temporary copies are made of the files to be edited
with the owner set to the invoking user.
2. The editor specified by the policy is run to edit the
temporary files. The sudoers policy uses the
SUDO_EDITOR, VISUAL and EDITOR environment variables
(in that order). If none of SUDO_EDITOR, VISUAL or
EDITOR are set, the first program listed in the editorsudoers(5) option is used.
3. If they have been modified, the temporary files are
copied back to their original location and the
temporary versions are removed.
If the specified file does not exist, it will be created.
Note that unlike most commands run by sudo, the editor is
run with the invoking user's environment unmodified. If,
for some reason, sudo is unable to update a file with its
edited version, the user will receive a warning and the
edited copy will remain in a temporary file.
-g group Normally, sudo runs a command with the primary group set to
the one specified by the password database for the user the
command is being run as (by default, root). The -g (group)
option causes sudo to run the command with the primary
group set to group instead. To specify a gid instead of a
groupname, use #gid. When running commands as a gid, many
shells require that the '#' be escaped with a backslash
('\'). If no -u option is specified, the command will be
run as the invoking user (not root). In either case, the
primary group will be set to group.
-H The -H (HOME) option requests that the security policy set
the HOME environment variable to the home directory of the
target user (root by default) as specified by the password
database. Depending on the policy, this may be the default
behavior.
-h The -h (help) option causes sudo to print a short help
message to the standard output and exit.
-i [command]
The -i (simulateinitiallogin) option runs the shell
specified by the password database entry of the target user
as a login shell. This means that login-specific resource
files such as .profile or .login will be read by the shell.
If a command is specified, it is passed to the shell for
execution via the shell's -c option. If no command is
specified, an interactive shell is executed. sudo attempts
to change to that user's home directory before running the
shell. The security policy shall initialize the
environment to a minimal set of variables, similar to what
is present when a user logs in. The CommandEnvironment
section in the sudoers(5) manual documents how the -i
option affects the environment in which a command is run
when the sudoers policy is in use.
-K The -K (sure kill) option is like -k except that it removes
the user's cached credentials entirely and may not be used
in conjunction with a command or other option. This option
does not require a password. Not all security policies
support credential caching.
-k [command]
When used alone, the -k (kill) option to sudo invalidates
the user's cached credentials. The next time sudo is run a
password will be required. This option does not require a
password and was added to allow a user to revoke sudo
permissions from a .logout file. Not all security policies
support credential caching.
When used in conjunction with a command or an option that
may require a password, the -k option will cause sudo to
ignore the user's cached credentials. As a result, sudo
will prompt for a password (if one is required by the
security policy) and will not update the user's cached
credentials.
-l[l] [command]
If no command is specified, the -l (list) option will list
the allowed (and forbidden) commands for the invoking user
(or the user specified by the -U option) on the current
host. If a command is specified and is permitted by the
security policy, the fully-qualified path to the command is
displayed along with any command line arguments. If
command is specified but not allowed, sudo will exit with a
status value of 1. If the -l option is specified with an l
argument (i.e. -ll), or if -l is specified multiple times,
a longer list format is used.
-n The -n (non-interactive) option prevents sudo from
prompting the user for a password. If a password is
required for the command to run, sudo will display an error
messages and exit.
-P The -P (preservegroupvector) option causes sudo to
preserve the invoking user's group vector unaltered. By
default, the sudoers policy will initialize the group
vector to the list of groups the target user is in. The
real and effective group IDs, however, are still set to
match the target user.
-p prompt The -p (prompt) option allows you to override the default
password prompt and use a custom one. The following
percent (`%') escapes are supported by the sudoers policy:
%H expanded to the host name including the domain name (on
if the machine's host name is fully qualified or the
fqdn option is set in sudoers(5))
%h expanded to the local host name without the domain name
%p expanded to the name of the user whose password is
being requested (respects the rootpw, targetpw and
runaspw flags in sudoers(5))
%U expanded to the login name of the user the command will
be run as (defaults to root unless the -u option is
also specified)
%u expanded to the invoking user's login name
%% two consecutive % characters are collapsed into a
single % character
The prompt specified by the -p option will override the
system password prompt on systems that support PAM unless
the passprompt_override flag is disabled in sudoers.
-S The -S (stdin) option causes sudo to read the password from
the standard input instead of the terminal device. The
password must be followed by a newline character.
-s [command]
The -s (shell) option runs the shell specified by the SHELL
environment variable if it is set or the shell as specified
in the password database. If a command is specified, it is
passed to the shell for execution via the shell's -c
option. If no command is specified, an interactive shell
is executed.
-U user The -U (otheruser) option is used in conjunction with the
-l option to specify the user whose privileges should be
listed. The security policy may restrict listing other
users' privileges. The sudoers policy only allows root or
a user with the ALL privilege on the current host to use
this option.
-u user The -u (user) option causes sudo to run the specified
command as a user other than root. To specify a uid
instead of a username, use #uid. When running commands as
a uid, many shells require that the '#' be escaped with a
backslash ('\'). Security policies may restrict uids to
those listed in the password database. The sudoers policy
allows uids that are not in the password database as long
as the targetpw option is not set. Other security policies
may not support this.
-V The -V (version) option causes sudo to print its version
string and the version string of the security policy plugin
and any I/O plugins. If the invoking user is already root
the -V option will display the arguments passed to
configure when sudo was built and plugins may display more
verbose information such as default options.
-v When given the -v (validate) option, sudo will update the
user's cached credentials, authenticating the user's
password if necessary. For the sudoers plugin, this
extends the sudo timeout for another 15 minutes (or
whatever the timeout is set to in sudoers) but does not run
a command. Not all security policies support cached
credentials.
-- The -- option indicates that sudo should stop processing
command line arguments.
Environment variables to be set for the command may also be passed on
the command line in the form of VAR=value, e.g.
LD_LIBRARY_PATH=/usr/local/pkg/lib. Variables passed on the command
line are subject to the same restrictions as normal environment
variables with one important exception. If the setenv option is set in
sudoers, the command to be run has the SETENV tag set or the command
matched is ALL, the user may set variables that would overwise be
forbidden. See sudoers(5) for more information.

PLUGINS

Plugins are dynamically loaded based on the contents of the
/etc/sudo.conf file. If no /etc/sudo.conf file is present, or it
contains no Plugin lines, sudo will use the traditional sudoers
security policy and I/O logging, which corresponds to the following
/etc/sudo.conf file.
#
# Default /etc/sudo.conf file
#
# Format:
# Plugin plugin_name plugin_path
# Path askpass /path/to/askpass
# Path noexec /path/to/noexec.so
#
# The plugin_path is relative to /usr/libexec unless
# fully qualified.
# The plugin_name corresponds to a global symbol in the plugin
# that contains the plugin interface structure.
#
Plugin policy_plugin sudoers.so
Plugin io_plugin sudoers.so
A Plugin line consists of the Plugin keyword, followed by the
symbol_name and the path to the shared object containing the plugin.
The symbol_name is the name of the struct policy_plugin or struct
io_plugin in the plugin shared object. The path may be fully qualified
or relative. If not fully qualified it is relative to the /usr/libexec
directory. Any additional parameters after the path are ignored.
Lines that don't begin with Plugin or Path are silently ignored
For more information, see the sudo_plugin(8) manual.

PATHS

A Path line consists of the Path keyword, followed by the name of the
path to set and its value. E.g.
Path noexec /usr/lib/sudo/sudo_noexec.so
Path askpass /usr/X11R6/bin/ssh-askpass
The following plugin-agnostic paths may be set in the /etc/sudo.conf
file.
askpass The fully qualified path to a helper program used to
read the user's password when no terminal is available.
This may be the case when sudo is executed from a
graphical (as opposed to text-based) application. The
program specified by askpass should display the
argument passed to it as the prompt and write the
user's password to the standard output. The value of
askpass may be overridden by the SUDO_ASKPASS
environment variable.
noexec The fully-qualified path to a shared library containing
dummy versions of the execv(), execve() and fexecve()
library functions that just return an error. This is
used to implement the noexec functionality on systems
that support LD_PRELOAD or its equivalent. Defaults to
/usr/lib/sudo/sudo_noexec.so.

RETURNVALUES

Upon successful execution of a program, the exit status from sudo will
simply be the exit status of the program that was executed.
Otherwise, sudo exits with a value of 1 if there is a
configuration/permission problem or if sudo cannot execute the given
command. In the latter case the error string is printed to the
standard error. If sudo cannot stat(2) one or more entries in the
user's PATH, an error is printed on stderr. (If the directory does not
exist or if it is not really a directory, the entry is ignored and no
error is printed.) This should not happen under normal circumstances.
The most common reason for stat(2) to return "permission denied" is if
you are running an automounter and one of the directories in your PATH
is on a machine that is currently unreachable.

SECURITYNOTES

sudo tries to be safe when executing external commands.
To prevent command spoofing, sudo checks "." and "" (both denoting
current directory) last when searching for a command in the user's PATH
(if one or both are in the PATH). Note, however, that the actual PATH
environment variable is not modified and is passed unchanged to the
program that sudo executes.
Please note that sudo will normally only log the command it explicitly
runs. If a user runs a command such as sudo su or sudo sh, subsequent
commands run from that shell are not subject to sudo's security policy.
The same is true for commands that offer shell escapes (including most
editors). If I/O logging is enabled, subsequent commands will have
their input and/or output logged, but there will not be traditional
logs for those commands. Because of this, care must be taken when
giving users access to commands via sudo to verify that the command
does not inadvertently give the user an effective root shell. For more
information, please see the PREVENTING SHELL ESCAPES section in
sudoers(5).

ENVIRONMENT

sudo utilizes the following environment variables. The security policy
has control over the content of the command's environment.
EDITOR Default editor to use in -e (sudoedit) mode if neither
SUDO_EDITOR nor VISUAL is set
MAIL In -i mode or when env_reset is enabled in sudoers, set
to the mail spool of the target user
HOME Set to the home directory of the target user if -i or
-H are specified, env_reset or always_set_home are set
in sudoers, or when the -s option is specified and
set_home is set in sudoers
PATH May be overridden by the security policy.
SHELL Used to determine shell to run with -s option
SUDO_ASKPASS Specifies the path to a helper program used to read the
password if no terminal is available or if the -A
option is specified.
SUDO_COMMAND Set to the command run by sudo
SUDO_EDITOR Default editor to use in -e (sudoedit) mode
SUDO_GID Set to the group ID of the user who invoked sudo
SUDO_PROMPT Used as the default password prompt
SUDO_PS1 If set, PS1 will be set to its value for the program
being run
SUDO_UID Set to the user ID of the user who invoked sudo
SUDO_USER Set to the login of the user who invoked sudo
USER Set to the target user (root unless the -u option is
specified)
VISUAL Default editor to use in -e (sudoedit) mode if
SUDO_EDITOR is not set

FILES

/etc/sudo.confsudo plugin and path configuration

EXAMPLES

Note: the following examples assume a properly configured security
policy.
To get a file listing of an unreadable directory:
$ sudo ls /usr/local/protected
To list the home directory of user yaz on a machine where the file
system holding ~yaz is not exported as root:
$ sudo -u yaz ls ~yaz
To edit the index.html file as user www:
$ sudo -u www vi ~www/htdocs/index.html
To view system logs only accessible to root and users in the adm group:
$ sudo -g adm view /var/log/syslog
To run an editor as jim with a different primary group:
$ sudo -u jim -g audio vi ~jim/sound.txt
To shutdown a machine:
$ sudo shutdown -r +15 "quick reboot"
To make a usage listing of the directories in the /home partition.
Note that this runs the commands in a sub-shell to make the cd and file
redirection work.
$ sudo sh -c "cd /home ; du -s * | sort -rn > USAGE"

SEEALSO

AUTHORS

Many people have worked on sudo over the years; this version consists
of code written primarily by:
Todd C. Miller
See the HISTORY file in the sudo distribution or visit
http://www.sudo.ws/sudo/history.html for a short history of sudo.

CAVEATS

There is no easy way to prevent a user from gaining a root shell if
that user is allowed to run arbitrary commands via sudo. Also, many
programs (such as editors) allow the user to run commands via shell
escapes, thus avoiding sudo's checks. However, on most systems it is
possible to prevent shell escapes with the sudoers(5) module's noexec
functionality.
It is not meaningful to run the cd command directly via sudo, e.g.,
$ sudo cd /usr/local/protected
since when the command exits the parent process (your shell) will still
be the same. Please see the EXAMPLES section for more information.
Running shell scripts via sudo can expose the same kernel bugs that
make setuid shell scripts unsafe on some operating systems (if your OS
has a /dev/fd/ directory, setuid shell scripts are generally safe).

SUPPORT

DISCLAIMER

sudo is provided ``AS IS'' and any express or implied warranties,
including, but not limited to, the implied warranties of
merchantability and fitness for a particular purpose are disclaimed.
See the LICENSE file distributed with sudo or
http://www.sudo.ws/sudo/license.html for complete details.